Coentrao pulled up mid-way through the first half when covering an Ajax counter-attack, and limped off moments later to be replaced by Portugal team-mate Pepe.

There was no immediate confirmation from the club as to the extent of the injury, but coach Jose Mourinho told reporters after the game that the change had been enforced.

"He felt something and had to come off," Mourinho said. "We will see what happens."

Coentrao's injury comes at a bad time for Mourinho, who is already without injured defenders Marcelo (broken foot) and Raul Albiol (ankle) until 2013.

Madrid Castilla defender Nacho, 22, may get another chance with the senior team at Valladolid's Estadio Jose Zorilla this weekend; alternatively, Rafael Varane may play at centre-back and Sergio Ramos at right-back, or on-loan Chelsea midfielder Michael Essien, himself just returning from an infection, may play in defence.

Coentrao has already missed a month of the current season through injury, after he suffered a groin problem on international duty against Russia in October.